Staphylococcus aureus is a gram-positive, facultatively aerobic, clump-forming cocci bacteria that commonly colonizes the nose and skin of healthy humans. Approximately 20-30% of the population is colonized with S. aureus at any given time. Staphylococcus aureus bacteria, sometimes also referred to as “staph”, “Staph. aureus”, or “S. aureus”, are considered opportunistic pathogens that cause minor infections (e.g., pimples, boils) and systemic infections.
Mucosal and epidermal barriers (skin) normally protect against S. aureus infections. Interruption of these natural barriers as a result of injuries (e.g., burns, trauma, surgical procedures and the like) dramatically increases the risk of infection. Diseases that compromise the immune system (e.g., diabetes, end-stage renal disease, cancer and the like) also increase the risk of infection. Opportunistic S. aureus infections can become serious, causing a variety of diseases or conditions, non-limiting examples of which include bacteremia, cellulitis, eyelid infections, food poisoning, joint infections, skin infections, scalded skin syndrome, toxic shock syndrome, pneumonia, osteomyelitis, endocarditis, meningitis and abscess formation.
S. aureus also can cause infection and disease in animals. For example, S. aureus frequently is associated with bovine mastitis.
S. aureus expresses a number of virulence factors, including capsular polysaccharides and protein toxins. One virulence factor often associated with S. aureus infection that is the major cytotoxic agent is alpha-toxin (also known as alpha-hemolysin or Hla), a pore-forming and hemolytic exoprotein produced by most pathogenic strains of S. aureus. The toxin forms heptameric pores in membranes of susceptible cells such as white blood cells, platelets, erythrocytes, peripheral blood monocytes, macrophages, keratinocytes, fibroblasts and endothelial cells. Alpha toxin pore formation often leads to cell dysfunction or lysis.